In fabricating complex circuits such as utilized in the telecommunication industry, vast arrays of circuit modules are interconnected with plug and socket type connectors. In many instances these plugs and sockets contain contact elements that are plated with very thin layers of gold or other precious metals to insure the electrical integrity of the engaged contact elements which interconnect the circuit modules. Obviously, repetitive insertion and withdrawal of the plugs during initial assembly, testing and subsequent utilization, erodes the gold plated surfaces. These complex circuit installations also contemplate the utilization of circuit boards which are provided with edge terminal fingers or contact pads which are insertable in socket-like receptacles containing spring contact fingers which run to terminals to provide the interconnections with other circuit boards, modules and power sources. Again, it is desirable to provide connectors for these types of installations wherein the contact elements are subject to a minimum amount of wear.
In more complex circuit configurations, a plurality of tiers of plugs are engaged within banks of individual socket-like connectors. Prior to shipment of such equipment to an installation, such as a telephone exchange, it is necessary to test the various circuits in the factory. Again, in conducting these tests, wear of the precious metal contacts of the plug and sockets should be held to a minimum. Inasmuch as these types of plugs and sockets have multitudes of contacting surfaces, a considerable amount of physical force is required in order to insert and withdraw the plugs from the sockets.
In recent years, connectors known as zero insertion force connectors have been developed to alleviate some of the wear problems, and reduce the amount of physical force required to assemble the connector plugs and sockets in operative relation. Examples of zero force connectors are shown in U.S. Pat. Nos. 3,963,317 issued June 15, 1976 to Eigenbrode, 4,047,782 issued Sept. 13, 1977 to M. L. Yaeger and 4,072,379 issued Feb. 7, 1978 to G. L. Towne et al. These patents are characterized by providing facilities for spreading a pair of rows of spring contacts to permit the insertion therebetween of a plug-like connector. The spreading is usually accomplished by interposing a camming member between a pair of rows of spring-like contact fingers. The camming member is rotated or shifted to spread the rows of spring contact pairs to permit the insertion of the plug-like connector, whereafter the camming member is again actuated to permit the spring contact pairs to flex into engagement with the plug contact elements.
Another type of zero insertion force connector arrangement is disclosed in U.S. Pat. No. 4,068,170 issued Jan. 10, 1978 to G. A. Chayka et al., wherein two banks of contact pairs are mounted on camming elements which are actuated to open the contact pairs to each bank. Two rows of leads depending from electronic components are inserted between the open banks of contact pairs, whereafter the camming members are turned to simultaneously close both banks of contact pairs against the depending leads. U.S. Pat. No. 3,670,288 issued June 13, 1972 to W. R. Evans shows a plurality of pretwisted parallel contact elements which are untwisted to provide spaces to receive terminals extending from a printed circuit board. Following insertion of the terminals, the contacts are returned to the pretwisted position to firmly engage the printed circuit board terminals.